1. Field of the Invention
The present invention relates to a fluid-transport machinery coupled in parallel, particularly to a system of energy-efficient and constant-pressure fluid-transport machines coupled in parallel.
2. Description of the Related Art
For recent years, owing to the advance of technology, the industrial products are growing precise, delicate and miniature more and more. To mass-produce those precise, delicate and miniature products in low cost, the current high-tech factories grow in scale continuously, and the quality requirements thereof also become more and more strict, which is a challenge for the building companies of the high-tech factory and the facility engineers who maintain the high-tech factory, and which also drives the related personnel to zealously research solutions or develop new technologies to fulfill the requirements.
In the current high-tech factories, it is a basic requirement for fluid-transport machinery to supply the gas and water of sufficient flow rate and stable pressure to every unit requiring them. When the factory is of smaller scale, merely a single fluid-transport machine is enough to supply the required flow rate. When only a single machine is used, the pressure stability can be easily and simply controlled according the operational manual provided by the manufacturer. However, in the current high-tech factories, the scale of the factory is enlarged continuously, and the fabrication procedures also become more and more flexible, in order to reduce the fabrication cost and to achieve the product diversification, and therefore, a single-machine fluid-transport system can no more meet the requirement. In order to supply the gas and water of sufficient flow rate and stable pressure to every unit requiring them and to shift the pressure and flow rate of gas and water as soon as possible and meet the new procedure's requirements when the fabrication procedures are changed, a system of multiple fluid-transport machines is needed in the current high-tech factories coupled in parallel. The operation of fluid-transport machines coupled in parallel is more complicated and crucial than that of a single fluid-transport machine, and just an imprudent operation may damage the machines. However, even the manufacturer cannot provide a standard operational procedure for the system of transport-fluid transport machines coupled in parallel. Thus, the factory-building companies and the facility-maintaining personnel can only depend on the experience accumulated in practical operation. The operational standard assumed in such a way is not only multitudinous and complicated but also neither analyzed theoretically nor verified experimentally. Therefore, it is hard to determine whether the assumed operational standard can achieve the required security and rapidity. The system of multiple fluid-transport machines coupled in parallel consumes considerable energy; therefore, reducing the consumed energy thereof can benefit the fabrication cost very much. However, the objective of saving energy cannot be realized via the current operational standard, which is assumed from individual experience.
When the user purchases a centrifugal fluid-transport machine, such as a pump, a blower, or an exhaust fan, the manufacturer will provide the user with operational data, such as the performance curves shown in FIG. 1. In FIG. 1, the horizontal and vertical axes respectively represent flow rate and pressure. The performance curve of maximum usable rotation speed begins from the vertical axis and ends in some point of the diagram, which represents the critical usable point. The area located at the right side of the performance curve of maximum usable rotation speed is a region unsuitable to use. According the Affinity Law of fluid-transport machines, the relationships with respect to rotation speed (N), flow rate (Q), pressure (P), and power (HP) are shown below.
                                                                                                              Q                    1                                                        Q                    2                                                  =                                                      N                    1                                                        N                    2                                                                                                                                                                P                    1                                                        P                    2                                                  =                                                      (                                                                  N                        1                                                                    N                        2                                                              )                                    2                                                                                                                                              HP                    1                                                        HP                    2                                                  =                                                      (                                                                  N                        1                                                                    N                        2                                                              )                                    3                                                                    }                            (        1        )            
Based on the data of the performance curve of maximum usable rotation speed, and via theoretical analysis and calculation, the following equations respectively relating pressure (P) with rotation speed (N) and relating pressure (P) with flow rate (Q) can be obtained.P=C1N2+C2N+C3  (2)P=C1Q2+C2Q+C3  (3)
Via equations (2) and (3), the performance curves of the rotation speeds lower than the maximum usable speed can be obtained, as the dashed curves shown in FIG. 1. Further, the equal-efficiency curves and the equal-power curves are also plotted in FIG. 1.
There are not many patents about the system of multiple fluid-transport machines coupled in parallel proposed before. The Taiwan Patent No. 506683 “Parallel-coupled Electrical Fans” discloses: a system of multiple parallel-coupled electrical fans, wherein multiple electrical fans are installed in parallel to a one-piece frame; however, it does not mention how to control the parallel-coupled electrical fans at all. As to the method of controlling the fluid-transport machine, the Taiwan Patent No. I225908 “Method of Controlling a Pump System” discloses: a method of utilizing automatic control and operational parameters of a centrifugal pump to pump fluid to an outlet; however, this patent is confined to the control of a single centrifugal pump, wherein pump rotation speed, water temperature, pressures at the inlet and outlet of the pump, and the pressure difference thereof detected by the sensors are compared with the pre-stored data, and then, the pump is adjusted according to the comparing result. The Taiwan Patent No. M253699 “Devices of Controlling a Pump System” discloses: a variety of devices of controlling a single centrifugal pump, which is similar to the previous patent. As shown in their claims, the abovementioned pre-stored data is not deduced from the theories but acquired via arranging the data gathered from practical operations; such a method advantages in that the states of a pump, which are to be the basis of control, can be easily and rapidly obtained; however, there are two constrains on such a method: one is that it cannot apply to the system of multiple parallel-coupled machines but can only apply to a single machine; the other is that the control range is limited by the pre-stored data. About energy efficiency, whether energy can be saved thereby is an unknown.
Accordingly, via theoretical analysis and experimental verification, the present invention proposes a system of energy-efficient and constant-pressure fluid-transport machines coupled in parallel and the operational method thereof, which not only can achieve the secure, rapid, and energy-efficient operation of the system of multiple fluid-transport machines coupled in parallel but also can unify and simplify the operational standard thereof, and the building cost thereof can also be lowered.